Funny--I haven't been on the forum in ages, but I guess I"m still subscribed to this thread!
We got the epoxy paint sprayed by a pro because we had a poor undersurface and it needed more work (the first coat led to a surface like an orange skin, which needed tons of sanding). However, the result is still the same: epoxy paint on an old fiberglass surface. It's been fine--but bear in mind, this tub does not get tons of use. I think tile doc is fine--it's the same stuff. Eventually, any surface will get scratches from use--when that gets too bad, it's time to sand it and resurface.